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| Titel |
Dependence of cloud properties derived from spectrally resolved visible satellite observations on surface temperature |
| VerfasserIn |
T. Wagner, S. Beirle, T. Deutschmann, M. Grzegorski, U. Platt |
| Medientyp |
Artikel
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| Sprache |
Englisch
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| ISSN |
1680-7316
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| Digitales Dokument |
URL |
| Erschienen |
In: Atmospheric Chemistry and Physics ; 8, no. 9 ; Nr. 8, no. 9 (2008-05-05), S.2299-2312 |
| Datensatznummer |
250006092
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| Publikation (Nr.) |
 copernicus.org/acp-8-2299-2008.pdf |
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| Zusammenfassung |
| Cloud climate feedback constitutes the most important uncertainty in climate
modelling, and currently even its sign is still unknown. In the recently
published report of the intergovernmental panel on climate change (IPCC), 6
out of 20 climate models showed a positive and 14 a negative cloud radiative
feedback in a doubled CO2 scenario. The radiative budget of clouds has
also been investigated by experimental methods, especially by studying the
relation of satellite observed broad band shortwave and longwave radiation
to sea surface temperature. Here we present a new method for the
investigation of the dependence of cloud properties on temperature changes,
derived from spectrally resolved satellite observations in the visible
spectral range. Our study differs from previous investigations in three
important ways: first, we directly extract cloud properties (effective cloud
fraction and effective cloud top height) and relate them to surface
temperature. Second, we retrieve the cloud altitude from the atmospheric
O2 absorption instead from thermal IR radiation. Third, our correlation
analysis is performed using 7.5 years of global monthly anomalies (with
respect to the average of the same month for all years). For most parts of
the globe (except the tropics) we find a negative correlation of effective
cloud fraction versus surface-near temperature. In contrast, for the
effective cloud top height a positive correlation is found for almost the
whole globe. Both findings might serve as an indicator for an overall
positive cloud radiative feedback. Another peculiarity of our study is that
the cloud-temperature relationships are determined for fixed locations
(instead to spatial variations over selected areas) and are based on the
"natural" variability over several years (instead the anomaly for a strong
El-Nino event). From a detailed comparison to cloud properties from the
International Satellite Cloud Climatology Project (ISCCP), in general good
agreement is found. However, also systematic differences occurred indicating
that our results provide independent and complementary information on cloud
properties. Climate models should thus aim to reproduce our findings.
Recommendations for the development of a "processor" to convert model
results into the cloud sensitive quantities observed by the satellite are
given. |
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